Photographic article with anti-static metal halide layer system of reducible optical density

ABSTRACT

A photographic article having a hydrophilic colloid coating located on a dielectric support is protected against the accumulation of static electrical charge by the provision of a layer system having a conductive layer with a surface resistivity of less than 1012 ohms per square. A protective layer formed of a metal halide overlies the conductive layer and, optionally, a second protective layer may be interposed between the conductive layer and the support. The layer system may be reduced in optical density by aqueous oxidizing solutions also useful in processing the photographic article following its exposure.

United States Patent 1191' Rasch et al. A

[54] PHOTOGRAPHIC ARTICLE WITH ANTI-STATIC METAL HALIDE LAYER SYSTEM OF REDUCIBLE OPTICAL DENSITY [75] Inventors: Arthur A. Rasch, Webster; Herbert B. Cowden, Rochester, both of N.Y.

[73] Assignee: Eastman Kodak Company,

Rochester, N.Y.

[22] Filed: May 23, 1972 [21] Appl. No.: 256,076

[52] US. Cl. 96/87 A, 96/1 R, 117/211, 117/106 [51] Int. Cl G03c 1/78 [58] Field of Search 96/87 A, 1.5, 1; 117/106, 117/211 [56] References Cited UNITED STATES PATENTS 2,939,787 6/1960 Giaimo 96/15 2,852,415 9/1958 Colbert et al.... 117/211 3,356,529 12/1967 Kiser et al...... 117/106 R [111 3,801,325 [451 Apr. 2, 1974 Primary Examiner--Norman G. Torchin Assistant Examiner-John L. Goodrow [57] ABSTRACT A photographic article having a hydrophilic colloid coating located on a dielectric support is protected against the accumulation of static electrical charge by the provision of a layer system having a conductive layer with a surface resistivity of less than 10 ohms per square. A protective layer formed of a metal halide overlies the conductive layer and, optionally, a second protective layer may be interposed between the conductive layer and the support. The layer system may be reduced in optical density by aqueous oxidizing solutions also useful in processing the photographic article following its exposure.

28 Claims, 3 Drawing Figures PHOTOGRAPHIC ARTICLE WITH ANTI-STATIC METAL HALIDE LAYER SYSTEM OF REDUCIBLE OPTICAL DENSITY This invention relates to an article having a hydrophilic colloid coating and a dielectric support which in-' corporates an anti-static layer system. In one aspect this invention relates to an article having an anti-static layer system comprised of a conductive layer and a selectively permeable protective layer. In a specific aspect this invention relates to a photographic article containing a radiation-sensitive material in which a hydrophilic colloid coating is bonded to a dielectric support and the resulting article is protected against static electrical discharge by an anti-static layer system.

Prior to this invention it has been recognized that in photographic structures incorporating a photosensitive emulsion coating on a dielectric support the accumulation of static charge on the support can have the undersirable effect when accidentally discharged of fogging the emulsion coating in the vicinity of the discharge. Static charge accumulation is particularly troublesome in roll films not containing gel pelloid layers or paper interleavers, as is frequently the case in film applications requiring minimal weight and/or rapid processing.

One approach that has been suggested in the art for dissipating or controlling static electrical charges on dielectric photographic supports involves the utilization of a thin metal coating having sufficient conductivity to prevent high, localized static charge accumulation. The principal disadvantages associated with metallic anti-static coatings are that when they are deposited in thin films of less than a few hundred angstroms they become oxidized during storage so that their conductances progressively decline and, hence, their antistatic properties deteriorate. If the metal coatings are applied in sufficient thicknesses to off-set their declining conductivities in the photographic environment, the increased thicknesses produce undesirable increases in optical densities. Some metals objectionably interact with photographic emulsion coatings to produce fogging and desensitizing thereof and some, such as bismuth and manganese, for example, will objectionably interact with the film support. A further disadvantage is that when a film support having a freshly deposited metal anti-static layer thereon is wound in reel forms, the metal frequently will adhere to both adjacent surfaces. When this occurs the metal may cause blocking, i.e., prevent unwinding of the reel or, if unwinding is in fact accomplished, the metal coating may be partially and randomly transferred to the opposite surface of the film support.

Prior to this invention it has been known to utilize metal and metal halide layers together in forming various types of optical articles, such as lenses, windows, Windshields and the like. For example, Scharf et al., U.S. Pat. No. 3,330,681, issued July 11, 1967, teaches reducing the reflection from a plastic optical article using a metal coating and a metal halide coating, while Colbert et al., U.S. Pat. No. 2,852,415, issued Sept. 16, 1958, teaches intimately mixing and grading the concentrations of metal and metal halide to achieve a coating of controlled conductivity and adherence to a siliceous surface. However, previously there has been no recognition that the disadvantages of metal anti-static layers in photographic articles can be obviated in whole or in part by utilizing anti-static layer systems incorporating conductive and selectively protective layers according to this invention.

It is an object of this invention to provide a photographic article including a dielectric support and a hydrophilic colloid coating that is protected against the accumulation of a static electrical charge by a layer system that is resistant to any reduction in its electrical conductivity during article storage and use and which is convertible to a less optically dense form during photographic processing.

It is further object to provide a photographic article incorporating an anti-static layer system which requires no special processing to reduce its optical density.

These and other objects of this invention are accomplished in one aspect by providing a photographic article comprising a radiation-sensitive material, a hydrophilic colloid coating for supporting the radiationsensitive material and a dielectric support for the hydrophilic coating. A layer system is bonded to the support comprising an electrically conductive layer exhibiting a surface resistivity of less than 10 ohms per square which is capable of oxidation to a less conductive, less optically dense state and a protective metal halide layer capable of retarding oxidation of the electrically conductive layer in the atmosphere and permeable to aqueous oxidizing solutions to permit oxidation of the electrically conductive layer thereby. The protective metal halide layer is bonded to a major surface of the electrically conductive layer remote from the support.

The protective layer effectively retards oxidation of the conductive layer during storage and/or use of the photographic article; however, being permeable to aqueous oxidizing solutions, the protective layer nevertheless permits the conductive layer to be oxidized to a less optically dense form during the processing of the article in ordinary aqueous photographic processing solutions, such as developing, fixing, bleach and/or stop baths. According to this invention it is then possible to obtain a photographic article that is protected against the accumulation of high, localized static electrical charge while the radiation-sensitive material associated with the hydrophilic colloid coating (hereinafter collectively designated as the radiation-sensitive colloid coating) is in a state capable of being adversely affected by a static electrical discharge. Also, a photographic article is obtained after processing in a final form that is free from the high optical densities heretofore associated with metal anti-static layers.

The anti-static layer system utilized in the practice of this invention is comprised of a binderless electrically conductive layer and one or more binderless protective layers. The term binderless layer refers to a layer that is substantially free of organic adhesive materials and refers particularly to the absence of those organic adhesive and binder materials commonly utilized in the photographic arts, such as natural and synthetic polymeric binders and colloidal vehicles.

The conductive layer may be comprised of any electrically conductive material which upon exposure to an aqueous photographic processing solution for the photosensitive emulsion coating is capable of being oxidized to a less optically dense form. It is immaterial whether the oxidation product is itself less optically dense or whether the layer is rendered less optically dense by the oxidation product being dissolved or partially dissolved in the photographic processing solution.

Because. of their high conductivities, metals are preferred for incorporation in the conductive layer. Manganese, bismuth, copper aluminum, and silver are exemplary metals that may be readily oxidized to less optically dense forms according to this invention when present as thin layers. Since it is specifically recognized that the conductive layer is in all cases separated by the protective layer from the radiation-sensitive colloid coating, metals may be chosen for the conductive layer that would be detrimentally reactive with the colloid coating if utilized alone, and, more specifically, metals that would, if used alone, fog or desensitize the radiation-sensitive colloid coating, may be utilized. Also, where a second protective layer is to be interposed between the support and the conductive layer, the metal chosen to form the conductive layer may be one which, if used alone or directly on the support, would objectionably interact therewith. For example, manganese and bismuth are both acceptable metals for the conductive layer even though both metals will fog a silver halide photosensitive emulsion coating when brought directly in contact therewith and will objectionably react with polymer film supports when deposited directly thereon.

In order to impart protection against the accumulation of static electrical charge it is necessary that the conductive layer exhibit a surface resistivity of less than 10 ohms per square. In photographic applications it is generally preferred that the conductive layer exhibit a surface resistivity of less 10 ohms per square. In order to insure that in all localized areas a surface resistivity of less than 10 ohms per square is attained it is preferred that the conductive layer portion have an overall surface resistivity of less than 10 ohms per square. With conductive layers having overall surface resistivities of less than ohms per square photographic reproductions may be uniformly and reliably obtained with no evidence of optical alterations attributable to localized discharge of static electrical charge.

As is well understood by those skilled in the art surface resistivity is determined by measuring the resistance between two parallel electrodes of a given length spaced apart by the same distance along a surface. Since an increase in the length of the electrodes tends to decrease the resistance observed by an amount equal to that by which the resistance would be increased by lengthening the spacing between the electrodes by a like increment, it is apparent that the electrode length and spacing are not material, so long as they are identical. Hence the surface resistivity expressed in ohms per square is a resistance measurement taken for the special case in which electrode length and spacing are identical and therefore mutually cancelling parameters.

The conductive layer is preferably formed no thicker than is required to yield the desired conductance characteristics. Such conductance levels can be obtained with metal conductive layer thicknesses of below 100 angstroms and, most preferably, below 50 angstroms. The purpose of limiting the conductive layer thickness is that, depending upon the material which is present in the conductive layer, the conductive material and/or one or more of its oxidation products may enter the aqueous photographic processing solution that is utilized both to process the radiation-sensitive colloid coating and simultaneously to render the conductive layer less optically dense. By limiting the content of the conductive layers the amount of material entering the processing solution from the photographic article is limited and the effectiveness and life of the processing solution is thereby prolonged. While the thickness of the conductive layer may be increased substantially above angstroms, depending upon the specific materials and/or oxidation products thereof entering the photographic processing solution as well as the volume and desired purity of the processing solution, layer thicknesses above about 1,000 angstroms are not required or contemplated for the particle of this invention.

A protective layer is directly bonded to the surface of the conductive layer remote from the substrate to protect the conductive layer from oxidation that will increase its surface resistivity during storage and use of the photographic article. In copending, commonly assigned application Rasch et al., Ser. No. 255,486, titled PHOTOGRAPl-IIC ARTICLE WITH COMPOSITE OXIDATION PROTECTED ANTI-STATIC LAYER, filed on May 23, 1972, is is recognized that a conductive layer may be protected against oxidation by employing one or more metal oxide protective layers. The metal oxide protective layers, however, unlike the protective layers of this invention, are not readily penetrable by aqueous photographic processing solutions. Accordingly, the conductive layer of the copending application is incorporated into the finished photographic article with its optical density essentially unaltered.

It is a surprising discovery of this invention that protective layers may be utilized which are capable of protecting the conductive layer against oxidation during storage and use of the photographic article and which also allow the conductive layer to be oxidized to a less optically dense form during the course of photographic processing in aqueous solutions. The present invention utilizes a protective layer for the conductive layer that is normally capable of retarding oxidation of the conductive layer, but which is selectively permeable to aqueous oxidizing solutions employed in photographic processing to permit reduction of the optical density of the conductive layer.

A protective layer having the desired selective permeability to aqueous oxidizing solutions can be a binderless layer of a metal halide (i.e., a metal fluoride, chloride or the like) and preferably consists essentially of a metal fluoride. Preferred metal halides are Group IIA and rare earth metal halides and, particularly Group [IA and rare earth metal fluorides. Cryolite (sodium aluminum fluoride) is also a preferred metal fluoride. The protective layer has a thickness of less than 500 angstroms and, most preferably, less than 50 angstroms, particularly where storage of the photographic article prior to processing in an aqueous oxidizing solution is anticipated. While the density of metal fluoride layers increases upon storage, metal fluoride layers of less than 50 angstroms are in all instances readily penetrable by aqueous oxidizing solutions. Substantially transparent (optical densities less than 0.01) metal halides are preferred with the protective layer in any case having an optical density of less than 0.5 where it is incorporated in the finished article. Where the protective layer is entirely removed in the course of photographic processing, as is generally the case, the optical density of the protective layer obviously does not influence the finished article.

In one form of the invention the conductive layer is bonded directly to the dielectric support and the protective layer is bonded directly to the conductive layer. In this way the support protects one major surface of the conductive layer while the protective layer protects the remaining major surface thereof. Where the support is itself permeable to oxidants and/or where the material forming the conductive layer is reactive with the support, it is preferred to interpose a second protective layer between the support and the conductive layer. The second protective layer may in one form be identical to the first protective layer. It is recognized that since the first protective layer is permeable to aqueous oxidizing solutions it is not necessary that the second protective layer be similarly permeable. Accordingly the second protective layer may be present in substantially greater thicknesses than the first protective layer, up to about 1,000 angstroms, but preferably less than 500 angstroms. The second protective layer may also be formed of a substantially insoluble metal oxide, such as silicon dioxide, silicon monoxide, alumina, magnesia, titania, boro-silicon oxide or tantalum oxide, as is disclosed in the above referenced copending application. The second protective layers should exhibit an optical density of less than 0.5. In the preferred form the second protective layer, like the first, is substantially transparent, i.e., exhibits an optical density of less than 0.01. Where the second protective layer is a metal halide that is removed during the course of photographic processing its optical density obviously does not influence the finished article.

The layer system utilized in the practice of this invention may be advantageously applied to any conventional photographic article support which is dielectric that is, which exhibits a surface resistivity in excess of at least ohms per square and, most commonly l0 ohms per square. Where the anti-static layer system is applied to any support of greater surface resistivity it will impart improved protection against the accumulation of static electrical charge.

Exemplary dielectric supports useful in the practice of this invention include supports such as glass, paper, wood, rubber and the like. Polymer supports and polymer coated supports are specifically contemplated. It is a surprising and useful feature of this invention that the protective and conductive layers of the layer system are readily adherent to hydrophobic polymer supporting surfaces. Typical hydrophobic polymers which form supporting surfaces according to this invention include cellulose esters such as cellulose nitrate and cellulose acetate; poly(vinyl acetal) polymers, polycarbonates, polyesters such as polymeric, linear polyesters of bifunctional saturated and unsaturated aliphatic and aromatic dicarboxylic acids condensed with bifunctional polyhydroxy organic compounds such as polyhydroxy alcohols, e.g. polyesters of alkylene glycol and/or glycerol with terephthalic, isophthalic, adipic, maleic, fumaric and/or azelaic acid; polyhalohydrocarbons such as polyvinyl chloride; and polymeric hydrocarbons, such as polystyrene and polyolefins, particularly polymers of olefins having from two to carbon atoms. The above polymers may be utilized in the form of flexible films or other unitary supports or may be utilized as coatings on glass, paper and polymer supports. A preferred class of coated supports is alpha-olefin resin coated paper supports, such as paper supports coated with polyethylene, polypropylene, ethylene-butene copolymers and the like.

Where the support presents a hydrophobic bonding surface to the hydrophilic colloid, it is typically coated with a subbing layer to improve the adhesion of the hydrophilic colloid coating to the hydrophobic surface. For example, polyester film supports, such as polyethylene terephthalate supports, are typically provided with a subbing layer comprised of a terpolymer of acrylonitrile of acrylate lower (less than four carbon atoms) alkyl esters, vinylidene halide and acrylic acid, such as, for example, acrylonitrile or methyl acrylate, vinylidene chloride and acrylic acid terpolymers. The layer system can be deposited over such subbing layers or can be deposited directly on the polymer film hydrophobic surface, since the metals that may be utilized to form the conductive layer as well as the metal oxides and fluorides that are employed to form the second protective layer are tenaciously adherent to such support surfaces.

The layer system may be deposited on the support utilizing techniques well understood by those skilled in the art. It is preferred to vacuum vapor deposit the conductive and protective layers onto the support. Vacuum vapor deposition is a readily controllable process wherein the thicknesses of the layers may be monitored and accurately controlled. Further, vacuum vapor deposition allows the protective layer to be deposited directly over the conductive layer without exposing the conductive layer to the atmosphere. This avoids the formation of even a minute oxide coating on the surface of the layer. It is observed that certain metals, particularly aluminum, when exposed to air readily form oxide coatings. These oxide coatings may interfere with subsequent oxidation of the conductive layer to reduce its optical density. For example, aluminum anti-static layers which are utilized without a protective layer according to this invention cannot be readily removed from dielectric supports or rendered transparent even when brought into association with aqueous alkaline solutions having a pH in excess of l I. By contrast aluminum conductive layers formed according to this invention by vacuum vapor deposition which are overcoated with a selectively permeable protective layer prior to extended exposure of the layer system to air can be readily rendered substantially transparent with ordinary aqueous alkaline photographic processing solutions-having a pH in excess of 9, but less than' 11. Thus, maintaining the conductive layer free of surface oxide can greatly improve the readiness with which its optical density is reduced.

The hydrophilic layer to be adhesively bonded to the dielectric support can be formed from one or more hydrophilic, water permeable colloid forming substances including both naturally occurring substances such as,

' for example, proteins such as gelatin and gelatin derivatives; cellulose derivatives; polysaccharides such as dextran, gum arabic and the like and synthetic polymer substances, such as water soluble polyvinyl compounds like poly(vinylpyrrolidone), acrylamide polymers and the like.

The hydrophilic colloids utilized can also contain other synthetic polymer compounds such as those which increase the dimensional stability of the colloid layers. Suitable synthetic polymers include those described, for example, in Nottorf US. Pat. No. 3,142,568, issued July 28, 1964; White US. Pat. No.

3,193,386, issued July 1965:,Houck et allLS Pat. No. 3,062,674, sailed Nov. 6, 1962; l-Iouck et al., U.S. Pat. No. 3,220,844, issued Nov. 30, 1965; Ream et al. U.S. Pat. No. 3,287,289, issued Nov. 22, 1966; and Dykstra U.S. Pat. No. 3,41 1,91 l, issued Nov. 19, 1968. Particularly effective are those water-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, those which have cross-linking sites which facilitate hardening or curing described in Smith U.S. Pat. No. 3,488,708, issued Jan. 6, 1970, and those having recurring sulfobetaine units as described in Dykstra Canadian Pat. No. 774,054.

The hydrophilic colloid can be hardened by various organic or inorganic hardeners, alone or in combination, such as the aldehydes and blocked aldehydes described in Allen et al. U.S. Pat. No. 3,232,764, issued Feb. 1, 1966, ketones, carboxylic and carbonic acid derivatives, sulfonate esters, sulfonyl halides and vinyl sulfonyl ethers as described in Burness et a1 U.S. Pat. No. 3,539,644 issued Nov. 10, 1970, active halogen compounds, epoxy compounds, aziridines, active olefins, isocyanates, carbodiimides, polymeric hardeners such as oxidized polysaccharides like dialdehyde starch and oxyguargum and the like.

Where the article formed is employed in forming an image by exposure to activating radiation, a hydrophilic colloid coating to be bonded to the support will contain in or on it a radiation-sensitive material. This material may be panchromatic or orthocromatic material, sensitive only to X-rays or sensitive to selected portions of the electromagnetic spectrum. In one form of the invention the radiation-sensitive portion of the photographic article can contain a single, unitary hydrophilic colloid layer having dispersed therein as an emulsion the radiation-sensitive material together with photographic addenda to form a radiation-sensitive emulsion coating, e.g., a photographic emulsion coating. In alternative forms the radiation-sensitive portion of the article can comprise a plurality of colloid coatings with the radiation-sensitive material or materials being contained in some or all of the coatings, but not necessarily in the hydrophilic colloid coating immediately adjacent the support or subbing layer. For example, as is characteristic of color photography, a plurality of radiation-sensitive colloid coatings can be present sensitized within separate segments of the visible spectrum. Typically, the hydrophilic colloid coating which immediately overlies the subbing layer (e.g., terpolymer layer) is itself free of radiation-sensitive material as coated. Typical hydrophilic colloid layers which can be bonded to a hydrophobic support surface but which contain no radiation-sensitive material, such as silver halide, when coated include, for example, antihalation layers, nucleated chemical transfer receiving layers, dye-mordant layers and the like.

Suitable radiation-sensitive materials which can be employed in practicing this invention are sensitive to electromagnetic radiation and include such diverse materials as silver salts, zinc oxide, photosensitive polycarbonate resins and the like. Silver halides are preferred radiation-sensitive materials and are preferably associated with a colloid or synthetic polymer dispersion vehicle to form an emulsion coating or layer. Silver halide emuslions can comprise, for example, silver chloride, silver bromide, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver chlorobromoiodide crystals or mixtures thereof. The emulsions can be coarse or fine grain emulsions and can be prepared by a variety of techniques, e.g., single jet emulsions such as those described in Trivelli and Smith The Photographic Journal, Vol. LXXIX, May, 1939 (pp. 330-338), double jet emulsions such as Lippmann emulsions, ammoniacal emulsions, thiocyanate or thioether ripened emulsions such as those described in Nietz et al U.S. Pat. No. 2,222,264, issued Nov. 19, 1940; lllingsworth U.S. Pat. No. 3,320,069, issued May 16, 1967, and McBride U.S. Pat. No. 3,271,157, issued Sept. 6, 1966. Negative type emulsions can be made, as well as direct positive emulsions as described in Leermakers U.S. Pat. No. 2,184,013, issued Dec. 19, 1939; Kendall et al U.S. Pat. No. 2,541,472, issued Feb. 13, 1951; Schouwenaars British Pat. No. 723,019, issued Feb. 2, 1955; lllingsworth et al. French Pat. No. 1,520,821, issued Mar. 4, 1968, lllingsworth U.S. Pat. No. 3,501,307, issued Mar. 17, 1970;1ves U.S. Pat. No. 2,563,785, issued Aug. 7, 1951, Knott et al. U.S. Pat. No. 2,456,953, issued Dec. 21, 1948 and Land U.S. Pat. No. 2,861,885, issued Nov. 25, 1958.

The silver halide emulsions employed in the articles of this invention can be sensitized with chemical sensitizers, such as with: reducing compounds; sulfur, sele' nium or tellurium compounds; gold, platinum or palladium compounds; or combinations of these.

The radiation-sensitive colloid coatings can additionally include a variety of conventional addenda both for the colloid and for the radiation-sensitive material. For example, photographic emulsion layers employed according to this invention may include development modifiers, antifoggants and stabilizers, plasticizers and lubricants, brighteners, spectral sensitization agents and color forming materials as set forth in paragraphs IV, V, XI, XIV, XV, and XXII, respectively, of Product Licensing Index, Vol. 92, Dec. 1971, publication 9232, pages 107-110. As previously indicated photographic articles of this invention can be processed with aqueous photographic processing solutions. Photographic articles containing the anti-static layer systems described herein can also be used in non-aqueous processing, e.g., in so-called dry processing systems. For example, the anti-static layer systems described herein can be used in silver halide containing articles designed for recording print out images as described in Fallesen U.S. Pat. No. 2,369,449 issued Feb. 18, 1945 or Bacon et al. U.S. Pat. No. 3,447,927 issued June 3, 1969; direct print images as described in Hunt U.S. Pat. No. 3,033,682 issued May 8, 1962 and McBride U.S. Pat. No. 3,287,137 issued Nov. 22, 1966; and articles designed for processing with heat, such as in articles containing an oxidation-reduction image-forming combination with a photosensitive metal salt such as a silver salt as described in Sheppard et al. U.S. Pat. No. 1,976,302 issued Oct. 9, 1934; Sorensen at al U.S. Pat. No. 3,152,904 issued Oct. 13, 1964 and Morgan et al. U.S. Pat. No. 3,457,075 issued July 22, 1969.

It is, of course, recognized that the photographic articles formed according to this invention can, if desired, incorporate antistatic or conducting layers other than or in addition to the inventive anti-static layer system. Such layers can comprise soluble salts, e.g., chlorides, nitrates, etc., ionic polymers such as those described in Minsk U.S. Pat. No. 2,861,056, issued Nov. 18, 1958, and Sterman et al., U.S. Pat. No. 3,206,312, issued Sept. 14, 1965, or insoluble inorganic salts such as 9 those described in Trevoy U.S. Pat. No. 3,428,451, issued Feb. 18, 1969.

In the course of processing after exposure photographic articles bearing radiation-sensitive colloid coatings are typically brought into association with alkaline and/or acid aqueous solutions, for example, developing baths, which are utilized for the purpose of silver reduction in silver halide emulsion coatings, typically exhibit a pH in excess of 9, while fixing baths, used for the purpose of dissolving silver halides from the colloid coating, typically exhibit a pH of less than 6.0 and, preferably, less than 5.0. It is a significant feature of this invention that these photographic processing solutions may be utilized to oxidize the conductive layer to a less optically dense form. While it has been heretofore recognized that certain metal anti-static layers are oxidized during the course of photographic processing, it is surprising that the conductive layers employed in this invention can be oxidized in these photographic processing solutions, since they are protected against oxidation during storage and use.

The manner and degree to which the optical density of the electrically conductive layer is reduced may vary, depending upon the aqueous oxidizing solution as well as the conductive and protective layer compositions and thicknesses chosen. In most instances both the conductive and protective layers are entirely removed from the support, so that there is no increase whatsoever in the optical density of the fully processed photographic article attributable to the anti-static layer system. While in some instances the protective layer may itself be dissolved by the aqueous oxidizing solution, as where a metal halide protective layer is dissolved by a complexing agent, such as a phosphate, contained in a processing solution, in most instances it is believed that the aqueous oxidizing solution first penetrates the protective layer and oxidizes the conductive layer. During the course of oxidation of the conductive layer its adhesion to the support is reduced so that both the protective and conductive layers are separated from the support. It is recognized that where the protective layer exhibits a low optical density, as is typical of metal halides, the protective layer may be left in place on the support. In such instances the conductive layer is also at least partially left in place on the support in an oxidized, less optically dense form. Where the layer system remains on the support after photographic processing it is preferred that it exhibit an overall optical density of less than 0.5. ln most instances the layer system is either entirely removed or rendered substantially transparent, i.e., exhibits an optical density of less than 0.01.

It is a further surprising feature of this invention that certain metals, such as aluminum, that are not normally oxidizable even on direct exposure by photographic processing solutions can be readily oxidized to a less optically dense 'state when utilized in conjunction with a protective layer that prevents oxidation of the aluminum in air. The advantages of both being able to stabilize the anti-static layer system during storage and use of a photographic article while reducing markedly its optical density in a fully processed article without introducing any additional processing steps or reactants are highly desirable and unexpected.

This invention may be better understood by reference to the drawings, which are fragmentary sectional views of photographic articles according to this invention as they appear prior to processing. For ease of illustration the various elements of the articles are not drawn to scale.

FIG. 1 illustrates a photographic article 1 comprised of a dielectric support 3, which is preferably a polymer film support. A layer system 5 overlies and is bonded to one major surface of the support. The layer system is comprised of a conductive layer 7 bonded directly to the support and a protective layer 9 which is bonded to a major surface of the conductive layer remote from the support. A subbing layer 11 is bonded to the opposite major surface of the support, and a photosensitive emulsion coating 13, is positioned over the subbing layer.

FIG. 2 illustrates a photographic article 15 which is identical to the photographic article 1, except that a subbing layer 17 is interposed between the conductive layer 7 and the support 3. Corresponding reference numerals are used to indicate corresponding elements.

FIG. 3 illustrates a photographic article 19 which differs from the articles 1 and 15 in that the subbing layer 11 is omitted between the emulsion coating 13 and the support 3. The layer system 21 is comprised of a conductive layer 23, a first protective layer 25, which is associated with a surface of the conductive layer remote from the support, and a second protective layer 27, which is interposed between the conductive layer and the support.

To further illustrate the invention the following specific examples are included:

EXAMPLE 1 To illustrate the superior stability of an antistatic layer system according to this invention as compared with an unprotected manganese metal layer, a roll of polyethylene terephthalate coated with a conventional subbing layer comprised of a terpolymer of acrylonitrile or methyl acrylate, vinylidene chloride and acrylic acid is loaded into a vacuum roll coater while magnesium fluoride is placed in a crucible within the coater for heating by an electron beam to provide a vapor source. The vacuum chamber is closed and pumped down to 3.2 X 10 Torr. The magnesium fluoride is heated in the electron beam of the vapor source to a point where it is subliming at a high rate. Shutters protecting the support from the magnesium fluoride are opened and the support drawn through the vapor at a rate such that the magnesium fluoride condenses on the substrate to a thickness of angstroms. After the roll of support is coated, the vapor source is cooled and the vacuum chamber returned to atmospheric pressure.

The coater is reloaded with the same roll and magne-' sium fluoride is removed from the vapor source and re placed with powdered manganese. The vacuum chamber is pumped down again, the vapor source is heated, and a layer of manganese is deposited over the magnesium fluoride. The layer of manganese is angstroms thick. Using the procedures above described a second layer of magnesium fluoride 50 angstroms thick is then deposited over the manganese layer on one half of the roll. In a similar manner a layer of manganese 60 angstroms thick is also deposited directly on an identical support roll.

Initially each of the coated supports exhibits a surface resistivity of less than 10" ohms per square. The manganese coated directly onto the support is entirely oxidized when stored overnight under ambient conditions. The support having the manganese deposited on magnesium fluoride but not overcoated exhibits a slight increase in surface resistivity when stored under ambient conditions for two weeks, whereas the support bearing the manganese layer that is both overcoated and undercoated with magnesium fluoride does not change in its surface resistivity characteristics. When the overcoated and nonovercoated supports are stored for 12 weeks 50 percent relative humidity and 50C, the overcoated sample increases slightly in surface resistivity; however, the surface resistivity remains below ohms per square. At the same time surface resistivity of the non-overcoated sample in which the manganese is deposited on magnesium fluoride increases to 10 ohms per square, which renders its surface resistivity unacceptably high to function as a protection against static charge accumulation. The acrylonitrile subbing layer samples exhibit initial surface resistivities of less than 10 ohms per square whereas the methyl acrylate samples exhibit initial surface resistivities of between 10 and 10 ohms per square. Otherwise the two subbing layers yield samples which are behaviorly comparable.

Each of the anti-static layer systems dissolve completely in less than one minute in an aqueous alkaline developer solution containing one part by weight pmethyl aminophenol for each four parts hydroquinone and having a pH of between 9 and 10, commercially available under the tradename Kodak D-19 developer. When a radiation-sensitive colloid coating such as a photographic emulsion coating is present on the support surface of the layer system, the layer system is removed during the development processing step without disturbing the processing of the photographic article or significantly altering the qualities of the resulting photographic article, except as protected from static discharge.

EXAMPLE 2 To illustrate the properties of an anti-static layer system according to this invention including bismuth as the conductive layer, a magnesium fluoride-bismuthmagnesium fluoride layer system is deposited on a cellulose acetate film support according to the procedure of Example 1, except that the bismuth and the magnesium fluoride overcoat are put on consecutively in a single run by using two electron beam vapor sources run simultaneously side by side. The thin film thus formed consists of a 50 angstron thick film of magnesium fluoride, a 70 angstrom film of bismuth, and a 50 angstrom thick overcoat layer of magnesium fluoride.

The layer system is not soluble in aqueous alkaline developer solutions, but is dissolved in less than 1 minute in a 2 percent acetic acid stop bath solution having a pH of less than 6. When fresh, the film has a resistivity of 4.2 X 10 ohms per square. After storage for 10 weeks at 50 percent relative humidity at 50C, the resistivity increases to 5.0 X 10 ohms per square. While this indicates some deterioration of the surface resistivity of the layer system, the final resistivity is still satisfactory to provide protection against surface charge accumulation. A radiation-sensitive colloid coating associated with the opposite surface of the support after layer system formation and before processing is protected against static electrical discharge and is not observably adversely affected by removal of the layer system during processing.

EXAMPLE 3 TABLE I Surface Resistivities- Thicknesses-angstroms Ohms --Per Sq.

Al Layers MgF, Layers Fresh 3 Months 8 Months 37 3l 25 700 34 62 65 1,800 4,000 40 83 40 320 2,600 66 38 25 58 22 35 200 2.0Xl0 10 All layer systems, except that having the least thick ness of aluminum, exhibit satisfactory surface resistivities at the end of eight months. However, even this layer system exhibits a satisfactory surface resisitivity at the end of three months storage and is therefore considered useable.

The layer systems described above are bathed at 23C in an aqueous alkaline solution of P-methyl aminophenol and hydroquinone having a pH of between 9 and 10 (Kodak D-l9 Developer) immediately after they are prepared and three months later. In addition, -a support with an unprotected aluminum layer is prepared and treated in the same manner. The times required to completely dissolve the layers are set forth in Table I].

TABLE 11 Time required to completely Layer system thicknesses dis olve layer system In each instance where the protective layer is less than 50 angstroms in thickness there is no observable increase in the time required to dissolve the layer system from the suppornwhere the protective layer is greater than 50 angstroms in thickness some slight increase in the time to remove the layer system is required. In comparing aluminum layers of like thickness it can be seen that the protective layer reduces the time for removal of the aluminum layer both when it is fresh and after three months storage. While it is noted that longer times are required to completely remove layer systems protected with magnesium fluoride protective layers of greater than 50 angstroms thickness, it is apparent from Table I that these layer systems exhibit satisfactory long term surface resistivity levels and are readily removed when fresh. Further, while these layer systems are not completely removed in less than minutes after three months storage, their optical densities are significantly reduced within this time period. Similar behavior is observed when aluminum is deposited onto a cellulose acetate film support. Since the aluminum is not reactive with film support materials, no protective underlayer between the support and aluminum layer is required. A silver chlorobromide gelatin emulsion coating associated with the supports after layer formation and before processing is protected from static electrical discharge where the surface resistivities are less than 10 ohms per square and is not observably degraded in photographic characteristics by the presence or removal of the anti-static layer system.

EXAMPLE 4 A silver film protected by magnesium fluoride is prepared in the following manner: A bell jar vacuum system equipped with an electron beam heated vapor source is provided with a set of rollers around which an endless belt prepared from a plastic film support can be fitted. Through a linkage and mechanical feed-through from the vacuum enclosure, the rollers can be driven from outside the vacuum chamber, and the belt can be drawn past an aperture in a mask situated between the bottom plane of the belt and the vapor source. This aperture is protected by a shutter, and the rest of the linkage is protected by suitable shields. A quartz crystal thickness monitor is used to monitor the rate of deposition.

A belt is made from a film of polyethylene terephthalate (PET) and placed in the vacuum system. Pure. silver is placed. in the crucible of the electron beam heated vapor source, and the chamber is pumped down to a pressure of 3.0 X 10 Torr. The silver is heated in the electron beam to the point of evaporation and the PET belt is driven at a rate of cycles per minute. The shutter over the aperture is opened and silver is deposited on the PET to a thickness of angstroms. The shutter is closed, the vapor source cooled, and the chamber is brought to atmospheric pressure.

Magnesium fluoride is placed in the crucible of the electron beam vapor source, and a mask is placed over the aperture so that only half the width of the support can be exposed. The chamber is pumped down to 3 X l0 Torr. and the PET is coated with a film of magnesium fluoride 50 angstroms thick using the technique described above.

When samples of the film are tested with respect to surface resistivities both when freshly formed and after storage for 6 weeks at 50 percent relatiyehumidity at 50C, results are obtained as set forth in Table III.

TABLE III Storage Properties Both sections of the film are insoluble in aqueous alkaline developer solutions, but both the unprotected silver and silver protected by magnesium fluoride are readily reduced in optical density by Kodak Ektachromebleach bath, which is an aqueous sodium ferricyanide bleach bath of a type described in U.S. Pat. No. 3,046,129. Silver halide that is deposited on the film during processing in the bleach bath is readily removed using Kodak F-5 Fixer, which is a sodium thiosulfate aqueous bath having a pH of less than 6. The anti-static layer system is then entirely removed from the photographic article during the course of photographic processing and does not contribute to the optical density of the finished photographic product. The magnesium fluoride protective layer does not inhibit the solution of the silver in the processing solutions.

EXAMPLE 5 described in Example 4. Cerous fluoride is then placed in the electron beam heated vapor source and a 200 angstrom film is deposited on half the width of the support. In a similar manner identical silver films are deposited and overcoated with a 400 angstrom film of calcium fluoride, a 300 angstrom film of barium fluoride, and a 400 angstrom film of aluminum sodium fluoride (cryolite). ln each case the metal fluoride overcoat protects the silver film against abrasion and against deterioration during storage. All films have a surface resistivity of less than 10 ohms per square, which ismore than sufficient to give the film excellent anti-static protection. The layer systems are insoluble in Kodak D-l 9 Developer, but are bleached in less than 10 seconds in Kodak Ektachrome Bleach. The silver bromide formed in the bleach bath dissolves in less than 5 seconds in Kodak F-S Fixing Bath.

Using the same general procedures described above copper conductive layers provided with a metal fluoride protective layer exhibit surface resistivities of below 10 ohms per square when freshly deposited and upon storage and are readily reduced'in optical density with aqueous oxidizing photographic processing solutions. Radiation-sensitive colloid coatings associated with support surfaces opposite the anti-static layer systems are protected in each instance from static electrical discharge and are not adversely photographically affected by the presence or removalduring processing of the layer systems.

What is claimed is:

1. In a photographic article comprising a radiationsensitive material, a hydrophilic colloid coating for supporting said radiation-sensitive material and a dielectric support for said hydrophilic colloid coating, the improvemnt comprising a layer system bonded to said support comprising an electrically conductive layer exhibiting a surface resistivity of less than ohms per square which is capable of oxidation to a less conductive, less optically dense state and a protective metal halide layer which consists essentially of said metal halide and is bonded to said electrically conductive layer, and is capable of retarding oxidation of said electrically conductive layer in the atmosphere and permeable to aqueous oxidizing solutions to permit oxidation of said electrically conductive layer thereby, said protective metal halide being binderless and bonded to a major surface of said electrically conductive layer remote from said support and having a thickness of less than 500 angstroms; the optical density of said metal halide layer being at most about 0.5.

2. A photographic article according to claim 1 in which said electrically conductive layer exhibits a surface resistivity of less than 10 ohms per square.

3. A photographic article according to claim 1 in which said electrically conductive layer exhibits a surface resistivity of less than 10 ohms per square.

4. A photographic article according to claim 1 in which said electrically conductive layer is comprised of an oxidizable metal.

5. A photographic article according to claim 4 in which said oxidizable metal is chosen from the group consisting of silver, aluminum, bismuth, manganese, and copper.

6. A photographic article according to claim 1 in which said protective metal halide layer is less than 50 angstroms in thickness.

7. A photographic article according to claim 1 in which said protective metal halide layer is comprised of a metal fluoride.

8. A photographic article according to claim 1 in which said metal halide protective layer is chosen from the group consisting of a Group IIA metal halide, a rare earth metal halide and cryolite.

9. A photographic article according to claim 1 additionally including as a part of said layer system a second protective metal halide layer interposed between said conductive layer and said support.

10. A photographic article according to claim 9 in which said second protective layer exhibits an optical density of less than 0.5.

11. A photographic article according to claim 9 in which said second protective layer is comprised of a compound chosen from the group consisting of metal oxides and halides.

12. A photographic article according to claim 1 in which said support is a polymer film.

13. A photographic article according to claim 12 in which said polymer film is comprised of a polyester.

14. A photographic article according to claim 12 in which said polymer film is comprised of polyalkylene terephthalate.

15. A photographic article according to claim 12 in which said polymer film is comprised of a cellulose ester.

16. A photographic article according to claim 12 in which said polymer film is comprised ofa cellulose ace tate.

17. A photographic article according to claim 12 in which a subbing layer is interposed between said polymer film and said hydrophilic colloid coating.

18. In a photographic article comprising a radiationsensitive material, a gelatin coating for supporting said radiation-sensitive material and a flexible dielectric polyester film support for said gelatin coating, the improvement comprising a vapor deposited anti-static layer system bonded to said support comprising an electrically conductive metal layer exhibiting a surface resistivity of less than 10 ohms per square which is capable of oxidation to a less conductive, less optically dense state and permeable oxidizing metal electrically a protective metal fluoride layer consisting essentially of said metal fluoride and having a thickness of less than 50 angstroms and being capable of retarding oxidation of said electrically conductive metal layer in the atmosphere and permeable to aqueous oxidizing solutions to permit oxidation of said electrically conductive metal layer thereby, said protective metal fluoride layer being binderless and bonded to a major surface of said electrically conductive metal layer remote from said support and having an optical density of at most about 0.01.

19. A photographic article according to claim 18 in which said support is polyethlene terephthalate.

20. A photographic article according to claim 18 in which said radiation-sensitive material is a silver salt.

21. A photographic article according to claim 18 in which said support is polyethylene terephthalate, said radiation-sensitive material is a silver halide and said metal fluoride is magnesium fluoride.

22. A photographic article according to claim 21 in which said silver halide is silver bromochloride.

23. In a photographic article comprising a radiationsensitive material, a gelatin coating for supporting said radiation-sensitive material and a flexible polyester film support for said gelatin coating the improvement comprising an anti-static layer system bonded to said support comprising an aluminum layer exhibiting a surface resistivity of less than 10 ohms per square and a protective layer consisting essentially of a metal fluoride chosen from the class consisting of Group IIA metal fluorides, rare earth metal fluorides and cryolite having a thickness of less than 500 angstroms; said protective layer having an optical density of less than 0.5.

24. A photographic article according to claim 23 in which said aluminum and protective layers are directly bonded and said aluminum layer is substantially free of any surface oxide associated therewith.

25. A photographic article according to claim 23 in which said metal fluoride is magnesium fluoride.

26. In a photographic article comprising a radiationsensitive material, a gelatin coating for supporting said radiation-sensitive material and a flexible polyester film support for said gelatin coating, the improvement comprising an anti-static layer system bonded to said support comprising a silver layer exhibiting a surface resistivity of less than 10 ohms per square and a protective layer consisting essentially of a metal fluoride chosen from the class consisting of Group lIA metal fluorides, rare earth metal fluorides and cryolite having a thickness of less than 500 angstroms; said protective layer having an optical density of less than 0.5.

27. In a photographic article comprising a radiationsensitive material, a hydrophilic colloid coating and a dielectric support for said hydrophilic colloid coating, the improvement comprising a binderless anti-static system comprising an electrically conductive layer having a thickness of less than 1,000 angstroms and a surface resistivity of less than ohms per square consisting essentially of a metal chosen from the class consisting of silver, aluminum, bismuth, manganese, copper and mixtures thereof and a protective layer having a thickness of less than 500 angstroms consisting essentially of a metal fluoride chosen from the group consisting of Group llA metal fluoride, rare earth metal fluoride and sodium aluminum fluoride; said protective layer having an optical density of less than 0.5. 28. In a photographic article comprising a radiationsensitive material, a hydrophilic colloid coating and a dielectric support for said hydrophilic colloid coating,

the improvement comprising a binderless anti-static layer system comprising a first protective layer bonded to said support having an optical density of less than 0.5 and consisting essentially of metal fluoride or oxide,

an electrically conductive layer having a thickness of less than 1,000 angstroms and a surface resitivity of less than 10 ohms per square consisting essentially of a metal chosen from the class consisting of silver, aluminum, bismuth, manganese, copper and mixtures thereof, said electrically conductive layer being bonded to said first protective layer from said support and a second protective layer having a thickness of less than 500 angstroms and an optical density of less than 0.5, and consisting essentially of a metal fluoride chosen from the group consisting of Group llA metal fluoride, rare earth metal fluoride and sodium aluminum fluoride.

P0405) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 801. 325 Dated Apri .1. 2 l 974 I Arthur A. Ras eh and Ho rho rt 1) Cowdon nventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 30, after "less insert -than--; Column 4 line l2 "particle" should read -practice--- Column 7 line '65; "em'guslions" should read ---emulsions--- Column 8, line 47, "18 should read ---l3- Column 12, lines 21-23;, the headings of Table I printed in the following manner:

Surface Resistivities Ohms Per'Sq.

3 Months 8 months should read:

- Su'rface Resistivities Ohms Per Sq.

Fresh 3 Months 8 Months Column 12 line 40 "lg-methyl" should read pmethyl-;

Column 14, lines 66-67, (Claim 1) "improvemnt" should read --improvement--;

Pow-0 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,801,325 T Dated April 2, 1.974 Inventor) Arthur A. Rasch and Herbert B. Cowden PAGE 2 It is certified that errofiappears in the above-identified batent and that said Letters Patent are hereby corrected as shown below:

Column 16, lines 10-11; "permeable oxidizing metal electrically" should be deleted;

"reeitivity" should read Column 18, line 7 -resistivity-.

y of September 1974.

Signed and sealed his 17th da (SEAL) Attest:

MCCOY-M. GIBSON JR. C. MARSHALL DANN Commissioner of Patents 'Attesting Officer 

2. A photographic article according to claim 1 in which said electrically conductive layer exhibits a surface resistivity of less than 108 ohms per square.
 3. A photographic article according to claim 1 in which said electrically conductive layer exhibits a surface resistivity of less than 105 ohms per square.
 4. A photographic article according to claim 1 in which said electrically conductive layer is comprised of an oxidizable metal.
 5. A photographic article according to claim 4 in which said oxidizable metal is chosen from the group consisting of silver, aluminum, bismuth, manganese, and copper.
 6. A photographic article according to claim 1 in which said protective metal halide layer is less than 50 angstroms in thickness.
 7. A photographic article according to claim 1 in which said protective metal haliDe layer is comprised of a metal fluoride.
 8. A photographic article according to claim 1 in which said metal halide protective layer is chosen from the group consisting of a Group IIA metal halide, a rare earth metal halide and cryolite.
 9. A photographic article according to claim 1 additionally including as a part of said layer system a second protective metal halide layer interposed between said conductive layer and said support.
 10. A photographic article according to claim 9 in which said second protective layer exhibits an optical density of less than 0.5.
 11. A photographic article according to claim 9 in which said second protective layer is comprised of a compound chosen from the group consisting of metal oxides and halides.
 12. A photographic article according to claim 1 in which said support is a polymer film.
 13. A photographic article according to claim 12 in which said polymer film is comprised of a polyester.
 14. A photographic article according to claim 12 in which said polymer film is comprised of polyalkylene terephthalate.
 15. A photographic article according to claim 12 in which said polymer film is comprised of a cellulose ester.
 16. A photographic article according to claim 12 in which said polymer film is comprised of a cellulose acetate.
 17. A photographic article according to claim 12 in which a subbing layer is interposed between said polymer film and said hydrophilic colloid coating.
 18. In a photographic article comprising a radiation-sensitive material, a gelatin coating for supporting said radiation-sensitive material and a flexible dielectric polyester film support for said gelatin coating, the improvement comprising a vapor deposited anti-static layer system bonded to said support comprising an electrically conductive metal layer exhibiting a surface resistivity of less than 108 ohms per square which is capable of oxidation to a less conductive, less optically dense state and permeable oxidizing metal electrically a protective metal fluoride layer consisting essentially of said metal fluoride and having a thickness of less than 50 angstroms and being capable of retarding oxidation of said electrically conductive metal layer in the atmosphere and permeable to aqueous oxidizing solutions to permit oxidation of said electrically conductive metal layer thereby, said protective metal fluoride layer being binderless and bonded to a major surface of said electrically conductive metal layer remote from said support and having an optical density of at most about 0.01.
 19. A photographic article according to claim 18 in which said support is polyethlene terephthalate.
 20. A photographic article according to claim 18 in which said radiation-sensitive material is a silver salt.
 21. A photographic article according to claim 18 in which said support is polyethylene terephthalate, said radiation-sensitive material is a silver halide and said metal fluoride is magnesium fluoride.
 22. A photographic article according to claim 21 in which said silver halide is silver bromochloride.
 23. In a photographic article comprising a radiation-sensitive material, a gelatin coating for supporting said radiation-sensitive material and a flexible polyester film support for said gelatin coating the improvement comprising an anti-static layer system bonded to said support comprising an aluminum layer exhibiting a surface resistivity of less than 108 ohms per square and a protective layer consisting essentially of a metal fluoride chosen from the class consisting of Group IIA metal fluorides, rare earth metal fluorides and cryolite having a thickness of less than 500 angstroms; said protective layer having an optical density of less than 0.5.
 24. A photographic article according to claim 23 in which said aluminum and protective layers are directly bonded and said aluminum layer is substantially free of any surface oxide associated therewith.
 25. A photogRaphic article according to claim 23 in which said metal fluoride is magnesium fluoride.
 26. In a photographic article comprising a radiation-sensitive material, a gelatin coating for supporting said radiation-sensitive material and a flexible polyester film support for said gelatin coating, the improvement comprising an anti-static layer system bonded to said support comprising a silver layer exhibiting a surface resistivity of less than 108 ohms per square and a protective layer consisting essentially of a metal fluoride chosen from the class consisting of Group IIA metal fluorides, rare earth metal fluorides and cryolite having a thickness of less than 500 angstroms; said protective layer having an optical density of less than 0.5.
 27. In a photographic article comprising a radiation-sensitive material, a hydrophilic colloid coating and a dielectric support for said hydrophilic colloid coating, the improvement comprising a binderless anti-static system comprising an electrically conductive layer having a thickness of less than 1,000 angstroms and a surface resistivity of less than 1012 ohms per square consisting essentially of a metal chosen from the class consisting of silver, aluminum, bismuth, manganese, copper and mixtures thereof and a protective layer having a thickness of less than 500 angstroms consisting essentially of a metal fluoride chosen from the group consisting of Group IIA metal fluoride, rare earth metal fluoride and sodium aluminum fluoride; said protective layer having an optical density of less than 0.5.
 28. In a photographic article comprising a radiation-sensitive material, a hydrophilic colloid coating and a dielectric support for said hydrophilic colloid coating, the improvement comprising a binderless anti-static layer system comprising a first protective layer bonded to said support having an optical density of less than 0.5 and consisting essentially of metal fluoride or oxide, an electrically conductive layer having a thickness of less than 1,000 angstroms and a surface resitivity of less than 1012 ohms per square consisting essentially of a metal chosen from the class consisting of silver, aluminum, bismuth, manganese, copper and mixtures thereof, said electrically conductive layer being bonded to said first protective layer from said support and a second protective layer having a thickness of less than 500 angstroms and an optical density of less than 0.5, and consisting essentially of a metal fluoride chosen from the group consisting of Group IIA metal fluoride, rare earth metal fluoride and sodium aluminum fluoride. 